sensors Review Non-Destructive Assessment of Chicken Egg Fertility Adeyemi O. Adegbenjo 1,2, Li Liu 1 and Michael O. Ngadi 1,* 1 Department of Bioresource Engineering, McGill University, 21, 111 Lakeshore Road, Ste-Anne-de-Bellevue, QC H9X 3V9, Canada; [email protected] (A.O.A.); [email protected] (L.L.) 2 Department of Agricultural and Environmental Engineering, Obafemi Awolowo University, Ile-Ife 220005, Osun State, Nigeria * Correspondence: [email protected] Received: 1 June 2020; Accepted: 13 July 2020; Published: 28 September 2020 Abstract: Total hatching egg set (for both egg production chicks and broilers) in the Agriculture and Agri-Food Canada report 2017 was over 1.0 billion. With the fertility rate for this year observed to be around 82%, there were about 180 million unhatched eggs (worth over 300 million Canadian dollars) incubated in Canada for the year 2017 alone. These non-hatching (non-fertile) eggs can find useful applications as commercial table eggs or low-grade food stock if they can be detected early and isolated accordingly preferably prior to incubation. The conventional method of chicken egg fertility assessment termed candling, is subjective, cumbersome, slow, and eventually inefficient, leading to huge economic losses. Hence, there is a need for a non-destructive, fast and online prediction technology to assist with early chicken egg fertility identification problem. This paper reviewed existing non-destructive approaches including ultrasound and dielectric measurements, thermal imaging, machine vision, spectroscopy, and hyperspectral imaging. Hyperspectral imaging was extensively discussed, being an emerging new technology with great potential. Suggestions were finally proffered towards building futuristic robust model(s) for early detection of chicken egg fertility. Keywords: chicken egg; non-destructive technologies; fertility identification; image analysis; machine vision; hyperspectral imaging 1. Introduction Over 50 billion chickens are being raised annually by poultry farmers all over the world, be it as layers towards egg production or as broilers towards meat production, and production growth is anticipated to continue. The global world population has been projected to hit 9.6 billion by 2050, creating an increasing demand for animal-based food [1]. Even though pork and beef demand could increase by up to 43% and 66% respectively, poultry meat has been projected to have the greatest growth rate of up to 121%, and demand for eggs is expected to increase by 65% [2]. For the year 2017, Canada exported over 39 million hatching eggs (worth over $68 million), with the US being the largest market. The importation figure for the same year however stood at over 141 million hatching eggs for broilers (worth over $49 million), with entire importation coming from the US (Agriculture and Agri-Food Canada report 2017). Seeing the great importance of chicken and chicken eggs both locally and globally, it is imperative especially in the present era of advancing technologies in the field of machine learning and artificial intelligence, that there would be worthwhile assistance towards improving the hatchability rate of chicken eggs. Early fertility (prior to incubation) and/or embryonic development detection would prevent wastage of egg and incubation energy, make more incubator space available for viable hatching eggs, and likewise promises huge economic returns. Achieving the above would be a crucial component of the effort on achieving the sustainable development goal 2 (SDG2) agendum. Sensors 2020, 20, 5546; doi:10.3390/s20195546 www.mdpi.com/journal/sensors Sensors 2020, 20, 5546 2 of 23 1.1. Egg Formation and Structure Egg formation is a process that occurs in about 25–26 h from ovulation to oviposition. It commences with a matured ovum (which is a plain yolk and germinal disc) in the reproductive tract, resulting at last in a hard shelled egg, fully complete with its own protective membranes and the necessary nutrients needed for embryonic development [3]. The major stages in egg formation include the ovulation stage, fertilization stage, formation, and oviposition. All these stages are accomplished in Sensors 2020, 20, x FOR PEER REVIEW 3 of 23 the ovary and the oviduct. The process can be better and clearly understood considering the schematic diagram in Figure1. Figure 1. Schematic diagram detailing the process of egg formation. In the ovary, the ovum or oocyte is released from the follicle through a process known as ovulation. Figure 1. Schematic diagram detailing the process of egg formation. Ovulation takes place in about 5 to 10 min following the expulsion of the previous egg. This stage has beenThe precededoviduct is with divided yolk into production six different made sections possible which from theare: chickens infundibulum (hens) (oviduct’s being fed withmouth diets or containingfunnel), magnum, appropriate isthmus, nutrients. shell Diets gland rich (uterus), in calcium vagina are of, goodand the necessity cloaca. at thisWhether stage asthe it ovum will find is usefulfertilized application or not (as later in the during case of the table shell or formation. hatchery infertile These nutrients eggs), it absorbedcontinues intoits journey the bloodstream along the fromoviduct the hens’to allow digestive for complete tracts are covering converted by into layers yolk byof theegg hen’s white liver. (albumen) The yolk and is then other transported internal throughsupporting the bloodstructures. stream The from section the liver of the to the oviduct ovary. responsible Here, the follicular for mos cellst of aroundalbumen the secretion ovum take is the yolkmagnum. and other The matured nutrients ovum and carry and its them surrounding along to the layers ovum. reaching The immature the magnum ova and can theirnow neighboringat this point follicularbe conveniently cells are called securely an egg embedded (if fertiliz withined, an embryo the ovary. is formed). As the ovum Due to increases the spiral in structural more and design more yolkof the accumulation, oviduct, the egg it becomes twists/rotates greatly along enlarged its journey so that and it can some no longerprotein fit fibers inside extension the ovary. from Therefore, the egg are hooked by the thick and thin albumens secreted along the oviduct. This occurrence results in albumen layers and chalazae formation. The shell membranes are then added in the Isthmus and the shell gland located in the uterus later commences the process of shell formation [5]. The average times, as reported by [6,7], an ovum spends in each section as it travels down the oviduct are: infundibulum 15 min, magnum 2–3 h, isthmus 1 h, uterus 21 h, and vagina/cloaca just a few minutes. A finally formed whole egg structure as shown in Figure 2 consists of 30–33% yolk, about 60% albumen, and between 9–12% shell [8,9]. The eggshell is deposited while the egg is still in the hen’s uterus. Three distinct stages of eggshell formation can be identified according to Hernández-Hernández, et al. [10] namely: (a) initial, Sensors 2020, 20, 5546 3 of 23 there begins a gradual continuous pushing of the nested ovum and the ovarian follicle towards the outer ovarian edge. As the ovum accumulates enough yolk that is adequate for growing a chick, the ovum ruptures from its follicle through a process earlier mentioned as ovulation. The free ovum drops into the ovarian pocket and within minutes is captured by the infundibulum and is guided into the mouth of the hen’s left oviduct. Almost immediately the ovum is released from the ovary and before being received by the infundibulum, the egg’s nucleus passes through a process of primary cell divisions known as meiosis and it is only one of the cells (others fade away naturally) produced from meiosis, which ends up becoming a matured ovum that is accepted by the infundibulum. Fertilization occurs inside the infundibulum if sperm is available, and the resulting zygote thereby commences a secondary cell division via mitosis. The first layer of albumen is also deposited at this stage [4]. The remaining process of egg formation is completed during the journey down the oviduct. The oviduct is divided into six different sections which are: infundibulum (oviduct’s mouth or funnel), magnum, isthmus, shell gland (uterus), vagina, and the cloaca. Whether the ovum is fertilized or not (as in the case of table or hatchery infertile eggs), it continues its journey along the oviduct to allow for complete covering by layers of egg white (albumen) and other internal supporting structures. The section of the oviduct responsible for most of albumen secretion is the magnum. The matured ovumSensors 20 and20, its20, x surrounding FOR PEER REVIEW layers reaching the magnum can now at this point be conveniently called4 of 23 an egg (if fertilized, an embryo is formed). Due to the spiral structural design of the oviduct, the egg(b) fast twists growth/rotates, and along (c) its termination. journey and The some initial protein stage fibers begins extension with fromcalcium the carbonate egg are hooked (CaCO by3) thespheruliths thick and forming thin albumens on the eggshell secreted membranes along the. oviduct.This formation This occurrence progresses results until adjacent in albumen spheruliths layers andare knitted chalazae (fuse formation.d) together The, a shellprocess membranes known as are nucleation then added. After in this the is Isthmus an emergence and the of shell columnar gland locatedcrystals in (palisades) the uterus laterfrom commencesthe spherules the during process the of shell fast formationgrowth stage. [5]. The Columnar average times,crystal as formation reported bycontinues [6,7], an until ovum eggshell spends calcification in each section is completed as it travels with down the the deposition oviduct are:of the infundibulum cuticle layer 15 in min, the magnumtermination 2–3 stage. h, isthmus It is important 1 h, uterus to 21 mention h, and vaginathat for/cloaca brown just eggs, a few deposit minutes.